1. Field of the Invention
The present invention relates to a substrate processing system configured to dispense a process liquid to a plurality of vertically arranged processing modules each processing a substrate with the process liquid. The present invention also relates to a method of controlling such a substrate processing system.
2. Description of Related Art
In a photo-lithographing step performed when manufacturing electronic devices such as semiconductors, an in-line process is conducted by using, in combination, a resist applying and developing apparatus, which is a unit apparatus for applying a resist liquid (hereinafter referred to as “resist”) to a substrate such as a wafer and developing the same, and an aligner, which exposes the substrate to which the resist has been applied. By subjecting a substrate to a series of processes, such as a cleaning process, dewatering and baking process, adhesion (hydrophobizing) process, resist applying process, pre-baking process, exposure process, baking process before developing process, developing process, and post-baking process, in this order, a predetermined circuit pattern is formed in a resist layer on the substrate. JP2000-235949A describes such an in-line process at the photolithographing step.
With a view to improving a production efficiency, the resist applying and developing apparatus includes a plurality of processing modules having the same processing function so as to simultaneously process a plurality of wafers. When all of these processing modules are horizontally arranged, the apparatus occupies an increased footprint. Thus, there is a tendency to vertically arrange the plurality of processing modules. As a result, a height of the overall apparatus recently reaches as high as about 3 meters.
The increased height of the overall apparatus by the vertically arranged processing modules produces an adverse effect on conditions of a resist (process liquid) discharged from nozzles (discharge pressure, discharge flow amount, discharge period, and so on) in a dispensing mechanism for dispensing the resist to the processing modules.
That is, in the conventional dispensing mechanism, pumps for supplying the resist to the nozzles and a bottle for containing the resist, or the like, are disposed near a bottom of the resist applying and developing apparatus, in order for facilitating a maintenance operation. However, this structure is disadvantageous in that, since pipings connecting outlets of the pumps with discharge ports of the nozzles vary in length in accordance with the corresponding processing modules, the resist is discharged from the nozzles to the respective processing modules at different pressures (the higher a position of the processing module is, the lower the discharge pressure becomes).
Although the same resist applying process is intended to be performed by the plurality of processing modules, the different resist discharge conditions of the respective modules may result in non-uniform film-thickness profiles of the applied resist. In order to cope with this situation, it is possible to set, with respect to each module, control parameters of the pump, and process conditions such as opening and closing timings of dispensing valve disposed upstream of the nozzle. However, if a defective film thickness profile of the resist is found after completion of the process, it takes a long time to search for a cause of such a trouble or manage the same, because all the parameters and conditions have to be verified.
In the conventional dispensing mechanism, a pump adapted to temporarily store a resist (process liquid) and deliver the same draws in and stores the liquid by its suction motion. Thus, the pressure in a piping on a pump suction side is reduced to a negative pressure. In this case, there is a possibility that a gas (e.g., nitrogen) dissolved in the resist forms micro bubbles because of the negative pressure. When the liquid includes the bubbles, the liquid may be undesirably, non-uniformly applied to a wafer.